Disable cadence rendering for low frame rate content.

The linked bug uses low frame count videos for animations, which
causes our cadence calculations to go wild trying to predict
a signal from limited data. Since low frame rate content isn't
hurt by being a frame or two off, just switch to coverage/drift
mechanisms in these cases.

R=eugene

Fixed: 445911484
Change-Id: I448aa958304862b76e2c229565bf2db75bec6268
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/6990716
Reviewed-by: Eugene Zemtsov <eugene@chromium.org>
Commit-Queue: Dale Curtis <dalecurtis@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1521651}